1. Field of the Invention
The present invention concerns a device to transmit and receive data for remote control of hearing devices, of the type having a transmission device with a transmitter coil to transmit data and a reception device with a reception coil to receive data.
2. Description of the Prior Art
A device of the above type is known from German OS 201 14 461, which serves as a transmission and/or reception unit for a hearing device for wireless data transmission between the hearing device and at least one external device. A number of transmission and/or reception coils are aligned in differing spatial directions.
Moreover, transponder antenna devices are known from German OS 44 31 446, in which a number of coils are used that are magnetically narrowly coupled with one another. Two or more coils that are arranged at a common core are thereby used for data transmission.
To transmit and receive signals in transceivers, coils preferably are used for the long-wave range, since signals in the long-wave range are predominantly inductively transmitted. Sufficiently strong fields must be generated for the inductive transmission.
It is technically difficult to realize, with sufficient transmission power, an oscillating circuit that is strongly energized from the outside with a fixed frequency when only very low supply voltages are available (as is the case, for example, in the remote control of hearing devices). For a strong field, a coil with many windings is necessary in order to achieve a sufficient field strength, but such coils have a high inductivity, and thus also a high alternating current impedance. The current that can be sent by the coil thus is significantly reduced, since the maximum current through the coil results from the quotient of the supply voltage and alternating current impedance.
In particular, coils with the most possible windings are necessary for the receiving circuit in order to generate the largest possible voltage from relatively weak fields. Such coils, however, are particularly poorly suited as transmitter coils to generate strong fields given low supply voltages. This problem ensues very particularly in the case of radio connections between two devices when relatively low frequencies are used, in the range of, for example, 50 to 500 kHz.
For a sufficiently high range of radio remote control, appropriately strong transmission fields are necessary. Should the radio remote control also be fashioned to receive data, a further coil or a further winding is additionally required for the reception. Such a receiver coil is, however, strongly overloaded (overdriven) by the field of the transmitter coil. Without protection, such as assembly can lead to the destruction of the receiver input stage.
To circumvent this problem, freely oscillating oscillator circuits can be used that re-excite themselves, and in which the voltages and therewith also the currents build up to higher values. Such oscillator circuits, however, oscillate at their resonant frequency and not exactly with the externally predetermined, desired frequency. As an alternative to this solution, the supply voltage can be distinctly increased in order to be able to force higher currents through the transmitter coil.